The invention relates generally to reclaiming bulk solid material, such as coal, from storage stockpiles or from watercraft such as barges and ships used to transport bulk material.
Bulk material reclaim is a serious concern, and typically requires costly equipment. As examples, on land, coal may be stored in piles next to a power plant, and must somehow be made to enter a conveyor system. Similarly, bulk material must be rapidly removed or “reclaimed” from piles to load a ship or a barge. Conversely, a ship or a barge, once it reaches its destination, must be unloaded. All sorts of processing plants store raw material in piles, which must efficiently be “reclaimed,” typically onto conveyors, for actual use. Thus, coal is just one example; the material can be any bulk material. Other examples are ore, wood chips, grain, and various food products.
In the field of bulk material reclaim, a term of art is “live” reclaim. “Live” reclaim refers to the material which comes out when a discharge gate is opened at the bottom of a stockpile. In most cases, due to “angle of reclaim,” material stops flowing long before the entire stockpile is recovered, forming a “reclaim cone” of empty space. The amount of material which inherently flows before a stable “reclaim cone” is formed and flow stops is referred to as the “live” reclaim. After that, a mechanical device must be employed to move the stored material towards the opening (such as a mechanical rake, or a bulldozer), or vibration applied to assist in the flow. Prior art vibration systems, such as “vibrating drawdown hoppers” from Carman Industries, are only a partial solution.
More particularly, storage and reclaim of large quantities of bulk material on land is presently handled by several general methods, each of which has its advantages, costs, and limitations.
A first method may be described as Open or Enclosed Storage with Under-storage Reclaim. Conical, windrow, kidney shaped, and other types of material piles are formed by a number of different methods. A reclaim tunnel is provided under the stored material, with openings on top of the reclaim tunnel through which the material falls onto a reclaim conveyor below. This method has the advantage of low capital cost. Its main disadvantage is that mobile equipment is required to move the material not directly over the openings into the openings. This is a time consuming, costly and hazardous activity.
A second method may be described as Covered Slot or Inverted Cone. Slot or inverted cone storage usually requires a cover to prevent the introduction of water. The inverted cone must be steep enough to allow the material to “self clean” and be equipped with a reclaim device. The slot must also be steep enough to “self clean” but, due to the geometry, the slot can be less steep than the cone. The slot requires a reclaim rotary plow. To achieve significant storage volume, both of these structures must be very large, require significant excavation, and significant capital cost. Due to the depth of inverted cones and slots, the reclaim conveyor is also usually expensive.
A third method may be described as On Grade Storage with Mechanical Reclaimers. This type of storage can be open or covered. Some of the mechanical reclaimers in use are (1) bucket wheel reclaimers, (2) portal reclaimers, and (3) drum type reclaimers. All of these reclaimers have a relatively high capital cost and significant operating cost. Very large storage areas make covered storage not practical, which can lead to environmental issues.
Reclaim of bulk material from barges and ships has always been a capital intensive, labor intensive, and time consuming activity. Recently, self unloading ships and barges with partial reclaim systems have been developed. The systems in use are very complicated and costly requiring a large number of drawdown points and a multitude of conveyors to maintain a reasonable ship or barge capacity.